The present invention relates to a rolling mill.
In rolling steel strip, mill rolls are deflected due to a rolling pressure generated between the mill rolls and the rolled strip; such roll deflection must be compensated. In the practical rolling operation, various rolled materials of different dimension and/or different quality are rolled by the same rolling mill and various rolling pressures are generated accordingly, so that the mill rolls are deflected in various ways; the compensation for such roll deflections is very difficult.
Modern rolling mills are required to produce rolled material having improved cross-sectional profile and flatness. Heretofore, in order to achieve such requirements, the "roll initial crown" method and the "roll bending" method have both been used in combination in the rolling operation. However, even when these two methods are used, satisfactory results have not always been obtained, since the "roll initial crown" method requires frequent replacement of the rolls and the "roll bending" method limits the bending force due to less strength of the roll chock and/or roll neck.
One solution proposed to solve the above-mentioned problems has been to use a rolling mill comprising a six-stand rolling mill with the intermediate rolls offset in their axial directions to control the deflection of the work rolls. However, installation of such a rolling mill is expensive and it is difficult to control the camber of the rolled material since the intermediate rolls are arranged asymmetrically with respect to the mill line and, further, the rolls wear rapidly. Also, conversion from a conventional four-stand rolling mill to a six-stand rolling mill requires several to ten days down time during which production is stopped. This adds substantially to production costs.
As an alternative solution, a variable crown roll has been proposed. The variable crown roll (referred to as "VC roll" hereinafter) comprises, as shown in FIG. 1 of the drawings, an arbor 1, a sleeve 2 and an annular clearance or space 3 formed between the arbor and the sleeve. The height of crown of the VC roll (i.e., radial expansion of the roll) can be controlled by supplying a medium (such as water, oil, grease or the like) under high pressure from a medium pressurizing unit 4 to the space 3 through a conduit 5 formed in the arbor 1 and by adjusting the pressure of the medium by the unit 4.
Conventionally, the VC roll has mainly been used in place of the backup roll of a multi-stand rolling mill and it has the merit that it is easy to change the height of the crown of the roll during the rolling operation. However, when a rolling reduction higher than that obtained by the conventional rolling operation is required, in some cases, the roll deflection can not be compensated only by controlling the height of the crown of the VC roll.
Recently, to increase the rolling efficiency and quality, a rolling mill which can realize a higher rolling reduction has been desired, preferably, one having a wider range of compensation for the roll deflection, and one in which it is possible to compensate for roll wear and/or the thermal crown.